A 24bit bitmap uses 4bytes/pixel (in average) in some sizes (1,2,3 pixels) to fill the dword boundary. When the dword boundary is filled with 3bytes/pixel (4 pixels), it will use 3 bytes/pixel, in other situations (5 pixels) the bytes/pixel is not constant. So a bitmap with 1,2,3 pixels will have the same size using 24bit or 32bit (4,8,12 bytes), a 4 pixels bitmap will use 12 bytes and 16 bytes respectively, a 5 pixels bitmap will have 16 and 20 bytes.
I also tested the performance of such issue. A program that bitblt 1000 times a 200x200 bitmap in a 32bit color display give the results below (an 77% overhead over 32bit bitmap). Attached is a program (used fpc 214, XP SP2, celeron D 1.4 512MB). In the other side 24bit bitmaps use less memory.
Although i disagree with the design/solution (using a 24bit bitmap by default in 32bit color display), that has performance issues and other side effects, the bitmap support improved with recent changes and i wont question this issue anymore, as the current LCL code.
The info here is just for clarify a misconception.PS: with the recent changes (using CreateDIBSection to create the bitmap) alpha blend in VTV under win32 i near ;-) .
Luiz
Bench24bit.rar
Description: Binary data
######################################## TChronoLog results - 2/9/2007 21:28:14 Session: 24bit first Results (6): microsec milisec seconds ------------------------------------- ----------- --------- --------- 0 - 24bit 263.699 264 0 1 - 24bit 263.957 264 0 2 - 24bit 262.954 263 0 3 - 32bit 148.656 149 0 4 - 32bit 148.796 149 0 5 - 32bit 148.833 149 0 Accumulated (Miliseconds): 1.237 ######################################## TChronoLog results - 2/9/2007 21:28:30 Session: 32bit first Results (6): microsec milisec seconds ------------------------------------- ----------- --------- --------- 0 - 32bit 149.329 149 0 1 - 32bit 149.110 149 0 2 - 32bit 148.376 148 0 3 - 24bit 263.509 264 0 4 - 24bit 263.677 264 0 5 - 24bit 264.157 264 0 Accumulated (Miliseconds): 1.238 ######################################## TChronoLog results - 2/9/2007 21:28:54 Session: Alternate Results (6): microsec milisec seconds ------------------------------------- ----------- --------- --------- 0 - 24bit 264.219 264 0 1 - 32bit 148.475 148 0 2 - 24bit 264.444 264 0 3 - 32bit 148.353 148 0 4 - 24bit 264.141 264 0 5 - 32bit 149.036 149 0 Accumulated (Miliseconds): 1.239
